Institute for Environmental Genomics, University of Oklahoma, Norman OK USA, Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK USA

Institute for Environmental Genomics, University of Oklahoma, Norman OK USA, Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK USA, University of Chinese Academy of Sciences, Beijing China

Institute for Environmental Genomics, University of Oklahoma, Norman OK USA, Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK USA, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing China

Institute for Environmental Genomics, University of Oklahoma, Norman OK USA, Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK USA, School of Ecological and Environmental Sciences, East China Normal University, Shanghai China

Institute for Environmental Genomics, University of Oklahoma, Norman OK USA, Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK USA, School of Minerals Processing and Bioengineering, Central South University, Changsha China

Thawing permafrost can stimulate microbial activity, leading to faster decomposition of formerly preserved organic matter and CO 2 release. Detailed knowledge about the vertical distribution of the responsible microbial community that is changing with increasing soil depth is limited. In this study, we determined the microbial community composition from cores sampled in a high Arctic heath at Svalbard, Norway; spanning from the active layer (AL) into the permafrost layer (PL). A special aim has been on identifying a layer of recently thawed soil, the transition zone (TZ), which might provide new insights into the fate of thawing permafrost. A uniquemore » sampling strategy allowed us to observe a diverse and gradually shifting microbial community in the AL, a Bacteroidetes dominated community in the TZ and throughout the PL, a community strongly dominated by a single Actinobacteria family (Intrasporangiaceae). The contrasting abundances of these two taxa caused a community difference of about 60%, just within 3 cm from TZ to PL. We incubated subsamples at about 5°C and measured highest CO 2 production rates under aerobic incubations, yet contrasting for five different layers and correlating to the microbial community composition. This high resolution strategy provides new insights on how microbial communities are structured in permafrost and a better understanding of how they respond to thaw.« less